happened and who is responsible. And the focus turning to the rebels. This evening, we go to the evidence. An intercepted phone call, and images in days and weeks leading up to the incident, including this wedding video. Brian Ross has this story. Reporter: Until now, the pro-russian rebels had welcomed all the attention they could get. Get. Even putting up billboards to support their claim. At this recent wedding of one of the fighters, the guest of honor was their top military commander, a Russian, not a ukranian, who now uses the name igor strelkov, which means igor the rifleman. We know he's had a longstanding relationship with the Russian intelligence services. Reporter: Under strelkov's command, the separatist militia fighting in Ukraine has been known as a ruthless gang of thugs. Well-armed and trained by the Russians, according to U.S. Intelligence officials. The Russian government is seeking deniability by employing covertly Russian ex-soldiers. Rambo-types. Reporter: Today, Ukraine released this footage it claims shows the actual sa-11 missile launcher near the scene right before the strike. U.s. Officials believe they made a mistake because they were not able to use the system. They made a mistake and shot down what they thought was another ukranian cargo plane. Reporter: In phone intercepts made public by Ukraine, one rebel thought it was a military plane that had been shot down. Ukraine officials say the rebel commanders realized their mistake, selling Russian officials it was a civilian aircraft, not military. Are there any weapons, one person asks. Nothing at all. Civilian belongings, medical scraps. Towels. Toilet paper. Told that the wreckage made clear it was a Malaysian airliner. Another person answers, well, then, it was bringing spies. Why were they flying? There's a war going on. Today, Ukraine officials released this video showing what they said was a surface-to-air missile battery in the same area as the crash being returned to Russia, with only two of its four missiles still onboard. Ukraine says that means the coverup is under way. And igor the rifleman is nowhere to be found. I want to bring in Martha Raddatz and colonel Steven --

This transcript has been automatically generated and may not be 100% accurate.

Who Are Pro-Russian Rebels Implicated in Missile Strike on Airliner in Ukraine?

Richard Clarke: "Core" of rebel group really Russian "dogs of war."

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